The invention relates to systems and methods for regulating peak electrical demand of temperature conditioning means for heating or cooling residential and other structures and for controlling indoor ambient temperature.
Increasingly residential and other structures are being heated and air conditioned by electrically energized temperature conditioning means, including air conditioners, heat pumps and resistance heating devices. Known types of thermostatic controls are commonly utilized to control such conditioning means so as to maintain desired indoor ambient temperatures.
The increasing utilization of such electrically energized temperature conditioning means imposes high electrical power loads on electrical utility systems during periods of extreme temperatures, i.e. air conditioning loads during summer months and heating system loads during winter months. Specific electrical load characteristics vary from one utility to another, due to differences in industrial loads and climatic conditions. However, it is established that utilities with large electrical heating loads will winter peak on the coldest days and those with air conditioning loads will summer peak on the warmest days. Extra generation and transmission capacity is needed for adequate supply of electrical power on these difficult days. Studies have confirmed a pattern of typical electric load peaks during winter and summer. It has been found that on extreme temperature days, electrical loads have a definite pattern of peaks and valleys throughout the day. Further these load patterns vary between the winter and summer peak months. For example, there may be a distinct morning peak and a separate distinct afternoon peak in the winter, whereas there may be a single afternoon peak in the summer.
It has been proposed to shift electric load demand from those peaks to provide some smoothing of the load demand imposed on the utility system. Adequate load shifting, i.e. power deferral, reduces peak demands and its undesirable effects.
Load shifting can be initiated with signals transmitted during peak periods by the utility company, e.g. by radio, carrier current or telephone. Alternate systems for interrupting the supply of electrical energy to loads during peak demand periods do not require the transmission of such signals. The supply of electric power to the loads during peak periods may be interrupted during predetermined time periods, based on the described historical load patterns, whenever outdoor temperature attains predetermined values. Thus power is deferred during these time intervals whenever the outdoor temperature attains predetermined values. Thus it has been suggested to interrupt power during specified time intervals in the winter when temperature is below a predetermined value, and in the summer when temperature is above a predetermined value.
Load deferral arrangements have been successfully utilized with limited types of loads. Electric hot water systems have been controlled in this manner. The success of this arrangement is largely attributable to the heat energy storage capability of the water, and to the acceptable range of temperature variation of the water. Power may therefore be interrupted for reasonable time periods without adverse user reaction.
Attempts have also been made to control the peak load demand of individual large buildings by large and complex control systems. These interrupt power solely in accordance to predefined rigid time schedules. Thus, for example, heating or cooling systems in different parts of a building are disabled for different interim time periods, e.g. up to 15 minutes every hour, based on the anticipated tolerance of the office occupants.
However, residential heating and air conditioning systems comprise a large portion of the utilities' peak loads during peak demand periods. Load deferral of such residential heating and cooling systems imposes substantial problems. Load deferral systems imposing discomfort on the owner or resident are unacceptable. The heat transfer coefficient of residences and their rooms differ drastically. Thus the heat energy required to maintain a predetermined indoor ambient temperature varies not only with variations between indoor and outdoor temperature, but also from residence to residence, and in some cases from room to room. Conversely interruption of the temperature conditioning means results in differing rates of temperature change. Interruption throughout the peak periods results in intolerable deviation of indoor temperature from the desired reference temperature. Even interruptions cycled on and off at a preestablished rate result in undesirable variations between different installations. Occupants of residences having high K factors and small capacity heating systems are exposed to greater, and thus objectionable, variations of indoor ambient temperature. Aside from these considerations, power deferral of residences can not be successfully provided by large and expensive control systems nor by systems that are difficult to install and to set up and control.